Surfactants and oils

By Brian de Villiers

 Surfactants and oils are probably two of the most misunderstood adjuvant groups. Their formulations are different, with surfactants being water soluble, while oils form an emulsion in water. The reason for the misunderstanding is because they have similar properties, namely retention, droplet spreading, and absorption. Therefore, they are often used interchangeably with poor results. Although these adjuvants have similar properties, they should be positioned with different crop protection products (CPPs). Product labels are often clear whether a surfactant or oil should be used, but costly mistakes are still frequently made.

Positioning

When a CPP registration holder decides whether to register a surfactant or oil with their product, a few important issues arise. Firstly, the formulation of the CPP must be considered. CPPs with water-soluble formulations, like the soluble liquids and granules, are often more effective with water-soluble surfactants. On the other hand, the oil-based CPPs with emulsifiable, suspension or other concentrates, often do better with an oil adjuvant. Secondly, tank-mixture components must be considered. If two CPPs are frequently applied in tank mixtures, but have conflicting adjuvant requirements, a compromise needs to be made. Then an adjuvant is normally selected that is beneficial to the most sensitive product, without antagonising the other CPP. Registration holders also take other factors into consideration, such  as phytotoxicity, environmental conditions, target weeds and crops. Therefore, it is vitally important to use the label recommended adjuvant because a lot of work has gone into the registration.

 
Exceptions to the rule

However, there are always exceptions to the rule. Sometimes, herbicides with specific formulations may be registered with the “incorrect” adjuvant, for example a surfactant instead of an oil. There could be many reasons for this. One reason could be to reduce the chance of phytotoxicity. Therefore, the surfactant may be slightly less effective than the oil on weeds, but it is also the safest option on the crop. It is vitally important to stick to the label recommended surfactant or oil. Failure to do so could result in inefficacy or, in rare cases, crop damage. There is normally a good reason for an adjuvant registration, therefore it is important to adhere to the label.

 
Villa’s stance

Surfactant and oil adjuvant use can be quite confusing. Do not increase the risk associated with a CPP application by using the incorrect adjuvant. Labels normally give a good indication of which adjuvants should be used. Contact your Villa agronomist for more information about adjuvants and water quality.